1. Field of the Invention
This invention relates to a personal watercraft which includes a saddle type seat extending in a forward and backward direction at a middle portion of a body, an operation handle member provided forwardly of the seat, and an arcuate keel provided at a middle portion of a bottom of the body.
2. Description of Background Art
One known example of a personal watercraft is a jet propulsion watercraft having a jet propeller mounted at a rear portion of a body and driven by an engine which takes in water from the bottom and jets the water rearwardly to propel the body.
This personal watercraft includes a keel provided at a middle portion of the bottom and extending forwardly and rearwardly (that is, from the bow to the stern).
FIG. 8 shows a sectional view of a conventional personal watercraft. The personal watercraft 100 is configured such that a keel 101 is formed in such a manner as to project downwardly so that it may project by a comparatively great amount downwardly from a middle portion of a bottom 102.
Since the keel 101 projects downwardly by a comparatively great amount, the straightforwardly advancing property of the personal watercraft 100 can be maintained suitably when it is propelled.
However, where the keel 101 projects downwardly by a comparatively great amount, for example, if the personal watercraft 100 is acted upon by a side wave while it glides, then the keel 101 is liable to be influenced by the side wave. Since the keel 101 is influenced by a side wave in this manner, the personal watercraft 100 tends to roll leftwardly or rightwardly.
An example of a personal watercraft which is not influenced by a side wave, is shown a xe2x80x9cPersonal Jet Propulsion Watercraftxe2x80x9d of the official gazette of Japanese Patent Publication No. Hei 6-96397. In the following, this personal watercraft is described in detail with reference to the succeeding figures (FIGS. 9 and 10) derived from FIGS. 1 and 4(A), respectively, shown in the official gazette. Note, however, that the reference numerals are re-numbered.
FIG. 9 is a sectional view showing a first example of a conventional personal watercraft which is less susceptible to being influenced by a side wave. The personal watercraft 110 is configured such that a keel 111 is formed flat so as not to project downwardly from a bottom 112.
According to this personal watercraft 110, even when it is acted upon by a side wave while it glides, the keel 111 is influenced comparatively little by a side wave. Therefore, the personal watercraft 110 does not roll leftwardly or rightwardly.
FIG. 10 is a plan view showing a second example of a conventional personal watercraft which is less susceptible to be influenced by a side wave. As a crew-member 115 of the personal watercraft 110 operates an operation handle member 116 as indicated by an arrow mark b, a steering nozzle (not shown) of a body rear portion 117 is swingably moved.
Consequently, a water jet 118 jetted from the steering nozzle is directed obliquely as indicated by an arrow mark c so that the personal watercraft 110 turns as indicated by an open arrow mark.
However, if the keel 111 is formed flat as not to be influenced by a side wave, then when the personal watercraft 110 is turned, the body is pushed by water from a sideward direction and the body tends to incline inwardly. However, since the bottom is formed flat, when the body begins to incline, the flat face of the body acts as resistance and the body is less likely to incline.
Therefore, it would be desirable to construct the personal watercraft 110 in such a manner that it could incline readily when the body begins to incline upon turning. With such a design, the personal watercraft 110 could be placed into a turning condition from a straightforwardly advancing condition, while maintaining a natural feeling for the operator, for example, similar to the natural feeling provided an operator of a motorcycle during a turning operation.
Therefore, the object of the present invention is to provide a personal watercraft which suitably assures a straightforwardly advancing property, and which also prevents the influence of a side wave, and inclines readily when the personal watercraft is turned.
In order to attain the object described above, according to the first aspect of the present invention, a personal watercraft is provided with a saddle type seat extending in a forward and backward direction at a middle portion of a deck of a body, an operation handle member provided forwardly of the seat, a pair of foot decks formed on the opposite sides of the seat, and a keel provided at a middle portion of a bottom of the body and extending from a bow to a stern. The keel extends in the forward and backward direction of the body and is formed in an arc. In addition, at a location rearward of the center of the body, the center of the arc of the keel substantially coincides with the height of the position of the center of gravity of the body.
At the portion of the body rearward of the center of the body, the center of the arc of the keel substantially coincides with the height of the position of the center of gravity of the body. Consequently, the radius of the arc of the keel can be made large. As the radius of the arc of the keel becomes large, the keel can be prevented from projecting downwardly by a great amount from the bottom. Since the projecting amount of the keel is suppressed in this manner, the keel is less likely to be influenced by a side wave so that the body can be prevented from rolling leftwardly or rightwardly by an influence of a side wave.
Further, since the center of the arc of the keel substantially coincides with the height of the position of the center of gravity of the body, when a crewmember performs a steering operation and the body turns its direction from a forwardly advancing direction to a turning direction and is pushed by water from a sideward direction, whereupon the body begins to incline toward the center of the turning movement, the body can incline around the height of the position of the center of gravity. Therefore, the body can incline readily when the watercraft turns.
Consequently, since the body can incline smoothly toward the center of the turning movement by a natural movement, the posture of the personal watercraft can smoothly change from an uprightly standing posture to an inclined posture when the watercraft is turned, providing an operator with the same sense as an operator of a motorcycle feels when the motorcycle turns.
According to a second aspect of the present invention, the radius of the arc of the keel gradually decreases forwardly at a location forward of the center of the body.
Since, at the portion of the body forward of the center of the body, the radius of the arc of the keel gradually decreases forwardly, the keel at the portion of the body forward of the center of the body can be made project by a comparatively great amount from the bottom.
Consequently, since the plowing property by the keel when the personal watercraft advances straightforwardly can be improved, when the personal watercraft is hit by a high wave during gliding thereof, the impact provided to the body can be kept low, and driving comfort can be maintained.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.